(1) Field of the Invention
This invention relates to an improved copying lens for use in copying machines and, more particulary, to an improved copying lens of small size to be used at or near unity magnification.
(2) Description of the Prior Art
In recent years, copying machines have found widespread use. In these machines, compact small-sized symmetrical lens sytems have been increasingly applied and adapted to the copying application with one of the aims being the correction of the various aberrations that occur at or near unity magnification.
In this kind of lens system there are many cases in which an aperture efficiency of about 100% is provided in order to prevent a decrease in the quantity of light at the edge of image plane. Because of this, a lens system design having a large angle of view will require an increased overall lens system length and an increased diameter for the outermost lens elements. Consequently, the manufacturing process for the respective lenses of the lens system becomes more difficult and the costs of the optical glass required to make the larger diameter and the costs associated with a large lens frame increase.
In view of the above, there is a need for a small-size compact means for properly correcting each of the aberrations in a lens system having a relatively wide angle view greater than 50.degree. at or near unity magnification. While various proposals have been made, a satisfactory arrangement had not yet been found.